Treatment of wells



Patented Oct. 14, 1941 UNITED; STATES PATENT OFFICE 2,259,428 TREATMENT or WELLS Paul G. Shelley, Midland, Mich., assignor to The Dow Chemical Company, Midland, M-icln.,-a corporation of Michigan No Drawing. Application apruzs, 1940, Serial No. 331,207

Claims.

The invention relates to the treatment of oil and gas wells with a fluid reagent to facilitate the production therefrom. It more particularly concerns an improved method of removing clogging deposits of paraffin, wax, and the like from the small pores and flow channelsof the producing formation of such wells.

It is well known that the porous formation constituting the oil and gas bearing stratum gradually becomes clogged with waxy asphaltic deposits commonly called paraflim as the well is produced. Heretofore it has been proposed to remove such clogging deposits from the pores and interstices of the producing formation by introducing into the well solvents of the type which are capable of at least partially dissolving the paraflin and like matter. Such solvents may be gasoline, petroleum naphtha, carbon atlin or constituents thereof. Such solvent can be forced deeply into the formation before it becomes warmed by contact with the formation to the extent that it will exert a solvent action lip on the waxy or asphaltic constituents of the paraiiin so as to become saturated with such tetrachloride, tetrachlorethylene and the like. a

In using such solvents, it is usually the practice to introduce the solvent into the well and force it into the surrounding formation where it is to act. However, theme of such solvents in the above manner has some serious disadvantages.-

remain in contact with the paraflin deposit, toy

that a portion of the dissolved paraflin reprecipitates, withthe result that the pores of the formation may again be plugged by the redeposited paraflin. disadvantage is especially pronounced when an attempt is made to-force the paraffin solvent deeply into the formation, due to the fact that thereis an opportunity for the solvent to become supersaturated as it is caused to contactadditional quantities of the paramn, and at the same time; there is more chance that reprecipitation will occur, due to the fact that the solvent comes in contact with a larger volume of oil or other fluid acting to dilute the solvent.

It is, thereforqan object of the invention to provide a method of treating wells with a pgrl aflin solvent whereby the action of the solvent onthe paraflinmay be substantially delayed or retarded, so that the solvent will exert substantially no solvent action during the time it is beirig forced into the formation,

Another object of the invention ls to provide constituents. Further, the solvent becomes ,diluted with the well fluids before it can act to disolve any considerable quantity of paraflln and thus its solvent power becomes substantially stable prior to becoming saturated with paraflin. After the solvent has been forced into the formation to the desired depth, it is held in place -by application of pressure, if necessary, until suflicient time has elapsedto allow the solvent to become warmed. The solvent becomes warm as it remains in contact with the earth formation, since the temperature ofgthe producing formations of oil and gas wells is usually between -l50 F. As the solvent becomes warmed, it attacks para fiin deposited in the for-.

mation causingfthe paraffln to disintegrate. The mixture then readily flows into the well bore through the flow channels which have been greatly enlarged by the action of the solvent. Since the cooled solvent does not immediately act to dissolve the constituents of the paraflin, saturation of the solvent first entering the formation is substantially prevented, and thus redeposition of the paraiiin from the solvent is largely susceptibleof control. 5

The temperature to which the solvent is to be cooled just prior to its introduction into the formation may vary, depending upon the depth the solvent is to be forced into the formation, and the ;temperature of the formation to be "treated; Ihave found that generally satisfactory results are obtainable by cooling the solvent to atemperature from between about 5 to -'20 C. It has-beenffound preferable in practice to coolthesolvent in the well bore just prior to its. introduction into the formation, for if an attempt is made to coolthe solvent at the earths surface and thereafter introduceit into the well, the solvent becomes warmed by the heating action of the well equipment and fluids contained in the well before it can reach the bottom of the well bore. On the other hand, cooling the solvent in the well bore just prior to its introduction into the formation results in the solvent entering the formation having the lowest solvent action possible during the time it is being forced to the desired location. Cooling of the solvent in the well bore'is accomplished by placing a quantity of ice, dry ice, or the like, depending upon the temperature desired, in the well bore, preferably after the well fluids have been removed" therefrom, as by .foroing them back into the formation, The solvent is then introduced into the well bore and allowed to come in contact with the cooling agent.

Incarrying out the method of the invention in a well, any liquid standing in the well bore is first preferably removed therefrom, as by forcing it back into the formation, or by bailing the well to remove such liquids. A quantity of the cooling medium is then placed in the well bore and the solvent introduced into the well through the tubing, if such be present. The solvent may be allowed to remain in contact with the cooling agent for a length of time calculated to produce the desired degree of cooling. After the desired amount of solvent has been introduced into the well, it may be displaced therefrom into the formation by applying a hydrostatic pressure thereon, as by pumping a fluid such as oil or water into the well on top of the solvent.

The amount of the solvent generally required to bring about the desired effect may vary, depending upon the depth the solvent is to be forced into the formation and the extent of the formation to be treated. I have found that generally satisfactory results are obtained by em- 'ploying 50-250 gallons or more of the desired solvent.

The solvent is held in place until sufficient time has elapsed for it to become warmed, or until it reaches the temperature of the formation and are allowed to return to the well bore and are.

removed therefrom, as by pumping the well or by a bailing operation.

If desired, the introduction of fresh solvent andwithdrawal of spent solvent may be repeated one or more times to insure a more thorough cleaning of the flow channels.

Among the advantages of the invention are that conventional paraflin' solvents may be employed to remove clogging deposits of paraffin from the flow channels of the formation without danger of the solvent entering the'formation becoming saturated with paramn while in an undiluted state so that the paraflin is later precipitated out of solution, plugging the pore channels of the formation; and that the paraffin deposited deeply in the pores and interstices of the formation maybe readily reached and removed by the solvent, because the solvent action of the paraffin has been retarded so that when it contacts the paramn deposited more deeply it still functions as a highly effective solvent.

llhis application is a continuation-in-part of my co-pending application Serial No. 215,228, filed June v22, 1938.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and distinctly claim as my invention:

' 1. In a method of treating a well to remove paraflln and the like, the steps which include introducing into the well bore a cooling agent, introducing a quantity of parafiin solvent into the well bore whereby the paraflin solvent is cooled by contact with said cooling agent, and thereafter forcing said cooled solvent into the surrounding formation.

2. In a method of treating a well to remove parafflnand the like, the steps which consist in introducing into the well bore a solid cooling agent, introducing into the well bore a quantity of paraflin solvent whereby the paraflln solvent is cooled by contact with said cooling agent, and

then forcing the cooled paraffin solvent into the surrounding formation.

3. In a method of treating a well to remove paraffin and the like, the steps which consist in introducing ice into the well bore, introducing into the well bore a quantity of paraflin solvent whereby the paraflin solvent is cooled by contact with the ice, and then forcing the cooled paraflln solvent into the surrounding formation.

4. In a method of treating a well to remove parafiin and the like, the steps which consist in introducing a quantity of solid carbondioxide into the well bore, introducing into the well bore a quantity of paraflin solvent whereby the par-. afiin solvent is cooled by contactwith the solid carbon dioxide, and thereafter forcing the cooled paraffin solvent into the surrounding formation.

5. In a, method Oftreating a well, to remove parafiin and the like, said well having liquid standing in the well bore, the steps which comprise removing the liquid from the well bore,-

introducing a cooling agent into the well bore,

thereafter introducing a paraflin solvent into the PAUL G. SHELLEY. 

